This invention relates to polyhydroxyethers, known as phenoxy resins, and their modification by grafting thereon moieties containing pendant carboxyl groups.
Phenoxy resins, sometimes referred to herein as "thermoplastic polyhydroxyethers," are known in the art as components of corrosion-resistant coatings, e.g., zinc-rich coatings for metallic substrates, as described in U.S. Pat. No. 4,370,382. Phenoxy-based coatings of the prior art are not, however, entirely satisfactory in that their adhesion to smooth substrates, e.g., metallic substrates, is subject to degradation by corrosion, particularly in environments of high humidity.
Carboxylic acids, particularly those with a hydrophobic hydrocarbon chain, are known to have corrosion inhibitive properties for steel exposed to near neutral salt solutions. Salts of weak acids, such as benzoic acid, have been used as corrosive inhibitors in boiler compounds and antifreeze solutions. However, organic acids, when used in coatings, often tend to migrate to the steel interface and interfere with the adhesion of the coating resin. It would be very useful, therefore, if a way could be found to realize the beneficial corrosion inhibiting effects of a carboxylic acid-containing coating, but without suffering the deleterious effects of the migration of the carboxylic acid.
It is also very desirable if, at the same time, the adhesion of a phenoxy-based coating could be improved, particularly under conditions of high ambient humidity.
Likewise, it would be desirable to provide compositions which can be readily emulsified in water, for use where solvent-free or minimum solvent systems are needed.
The carboxylic acid-containing phenoxy resins of this invention can be used as general purpose and corrosion resistant coatings, and particularly for highly pigmented systems such as zinc-rich and magnetic media coatings. These resins have improved dispersing properties for particulate materials, such as powders. They may be used in adhesives and laminating systems with improved wet adhesion, and particularly for polar and metallic substrates. The resins are also useful in water-dispersible coatings, adhesives and laminating systems.
All these commercially important objectives are met by the present invention.